Electrochemical immunosensor for the breast cancer marker CA 15-3 based on the catalytic activity of a CuS/reduced graphene oxide nanocomposite towards the electrooxidation of catechol

The authors report on an electrochemical immunosensor for the tumor marker carbohydrate antigen 15-3 (CA15-3). It is based on the use of a composite consisting of reduced graphene oxide (RGO) and copper sulfide (CuS) that was placed on a screen-printed graphite electrode. The electrode shows excellent activity towards the oxidation of catechol acting as an electrochemical probe, best at a working potential of 0.16 V. The electrode was modified with antibody against CA15-3. Once the analyte (CA15-3) binds to the surface of the electrode, the response to catechol is reduced. The assay has a linear response in the 1.0-150 U mL(-1) CA15-3 concentration range, with a 0.3 U mL(-1) lower detection limit and a sensitivity of 1.88 mu A mu M-1 cm(-2). The immunosensor also shows good reproducibility (2.7%), stability (95% of the initial values after storing for four weeks). The method was successfully applied to the determination of CA15-3 in serum samples, and results were found to compare well to those obtained by an ELISA. Conceivably, this nanocomposite based detection scheme has a wider scope and may be applied to numerous other immunoassays.